Circadian Rhythm and the Seasonal Variation in Childhood Febrile Seizure

Objective We aimed to assess the circadian rhythm and the seasonal variation in childhood febrile seizure (FS). Materials & Methods This descriptive cross-sectional study was conducted retrospectively on patients’ records. Investigators assessed the records of patients with simple FS aged 6 to 60 months referred to Emergency Department of 17-Shahrivar Hospital, Rasht northern Iran during Jan 2010 to Jan 2013. Data were gathered by a checklist including age, sex, temperature, duration of seizure, seasonal, months, diurnal variation, and level of consciousness. Results Totally, 349 patients including 193 (55.3%) boys and 156 (44.7%) girls with the mean age of 22.85±18.34 months were enrolled in this study. The mean temperature of patients was 38.45±0.53°C. The mean duration of seizure was 97.91±57 sec. Awake, drowsy and slept patients were noted in 170 (48.7%), 33(9.5%) and 146 (41.8%) cases, respectively. Most of the FS occurred in winter 118 (33.8%), afternoon 132 (37.8%) and in Jan 55 (15.8%). Conclusion Body temperature adjusted by hypothalamus affecting by circadian rhythm. FS is the most common form of seizure in childhood occurred by multifactorial issues. Otherwise, the occurrence of seizure in patients with epilepsy may be affected by the circadian rhythm. Seizures happen more frequent at a specific time in 24 h during a day.


Results
Totally, 349 patients including 193 (55.3%) boys and 156 (44.7%) girls with the mean age of 22.85±18.34 months were enrolled in this study. The mean temperature of patients was 38.45±0.53°C. The mean duration of seizure was 97.91±57 sec. Awake, drowsy and slept patients were noted in 170 (48.7%), 33 (9.5%) and 146 (41.8%) cases, respectively. Most of the FS occurred in winter 118 (33.8%), afternoon 132 (37.8%) and in Jan 55 (15.8%). conclusion Body temperature adjusted by hypothalamus affecting by circadian rhythm. FS is the most common form of seizure in childhood occurred by multifactorial issues. Otherwise, the occurrence of seizure in patients with epilepsy may be affected by the circadian rhythm. Seizures happen more frequent at a specific time in 24 h during a day.

ORiGinaL aRTicLe introduction
Febrile seizure (FS) is the most common form of pediatric seizure, which occurs in 2%-5% of children. Eighteen months old is the estimated peak age for its occurrence (1). FS is defined as the seizure with febrile illness during 6-60 months of age, which does not happen because of central nervous system infection or metabolic disorders. Children do not have any history of afebrile seizures (2) (4) December 42 (12) of this age-dependent seizure. Commonly most of the patients report the familial history of febrile seizure. Usually, in most patients with positive familial history, FS happens as an autosomal dominant disease (2). Otherwise, core body temperature has circadian rhythm during 24 h which varies from 36.5 °C (early morning) to 37.5 °C (early evening) (4). Specific cells in hypothalamus control the body temperature that varies by circadian rhythm. This rhythm emerges from at least 1 months of age in children (5). From 18 months of age, the duration of morning nap gradually decreases and 6 yr old child has only nocturnal sleep (6), the circadian rhythm works properly during the specific age of FS (6 to 60 months) (5). Epileptic seizures occur mostly in some specific time of the day (7). The seizures occurrence depends on circadian rhythm. Circadian rhythm and the secondary cyclic changes in hormones and the sleep-wake cycles can have potential effect on the time of seizures occurrence (8).
Regarding the clinical experiences, the increased rate of seizure in patients with epilepsy may be associated with the nocturnal melatonin rise. Although the pharmacological level of melatonin prohibits the occurrence of seizure, the physiologic level of this hormone can induce seizure by inhibiting effect on dopaminergic system (inhibit seizure) (9). Furthermore, FS can be affected by seasonal variation (10)(11)(12)(13).
In this study, we aimed to assess the circadian rhythm and the seasonal variation in childhood febrile seizure.

Materials & Methods
This descriptive cross-sectional study was conducted retrospectively on patients' records.  (10). In this study, the highest frequency of FS occurred at winter and in January. This was similar to other results (11)(12)(13). This higher frequency may be because of higher frequency of febrile illness and infections during winter.
Most of the patients were awake during FS. Nevertheless, there were no previous investigations assessing the level of consciousness in patients. The incidence of FS was higher in specific seasons and months (especially during the winter), certain times of the day, and certain sleep-awake states. As daily and long-term anticonvulsant therapy is not allowed due to its complications in childhood because could not prevent the occurrence of epilepsy, the best way to prevent febrile seizures is to administer diazepam at the time of the febrile illness. in conclusion, parents should be advised on taking more care of febrile illness in certain months, seasons or at certain times of the day and in certain sleep-wake states. They should prevent febrile seizures by prophylactic administration of diazepam (due to short-term effect of diazepam).

acknowledgments
We acknowledge the cooperation of our colleagues. This study was done with financial support provided by Vice Chancellor of Research, Guilan University of Medical Sciences.

author's contribution
Sharafi R: Conceptualized and designed the study, coordinated and supervised data collection, drafted the initial manuscript and reviewed and revised the manuscript. Hassanzadeh Rad A: Conceptualized and designed the study, drafted the initial manuscript and reviewed and revised the manuscript. Aminzadeh V: Conceptualized and designed the study, coordinated and supervised data collection, drafted the initial manuscript and reviewed and revised the manuscript.
All authors agreed to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.